Certain abbreviations that may be found in the description and/or in the Figures are herewith defined as follows:    3GPP Third Generation Partnership Project    CAZAC constant-amplitude zero auto-correlation    CDF cumulative distribution function    CDM code division multiplexing    CDMA code division multiple access    CM cubic metric    CP cyclic prefix    CQI channel quality indicator    DFT discrete Fourier transform    DFT-S-OFDM discrete Fourier transform spread OFDM (SC-FDMA based on frequency domain processing)    eNode B E-UTRAN Node B (eNB)    E-UTRAN evolved UTRAN    FDM frequency division multiplexing    FDMA frequency division multiple access    FFT fast Fourier transform    IFFT inverse FFT    LB long block    LTE long term evolution of UTRAN (E-UTRAN)    Node B base station    OFDM orthogonal frequency division multiplexing    OFDMA orthogonal frequency division multiple access    PAR peak to average ratio    PRB physical resource block    PUCCH physical uplink control channel    PUSCH physical uplink shared channel    QPSK quadrature phase shift keying    RAZAC random zero auto-correlation    RRC radio resource control    SC subcarrier    SC-FDMA single carrier, frequency division multiple access    SNR signal to noise ratio    UE user equipment, such as a mobile station or mobile terminal    UL uplink    UTRAN universal terrestrial radio access network    ZC Zadoff-Chu
A proposed communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE) is currently under discussion within the 3GPP. The working assumption is that the DL access technique will be OFDMA, and the UL technique will be SC-FDMA.
Reference may be made to Section 6 of 3GPP TR 36.211, V1.0.0 (2007-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Channels and Modulation (Release 8) for a description of the UL physical channels.
Reference may also be made to 3GPP TR 25.814, V7.1.0 (2006-09), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical layer aspects for evolved Universal Terrestrial Radio Access (UTRA) (Release 7), such as generally in section 9.1, for a description of the SC-FDMA UL of E-UTRAN.
FIG. 1A reproduces FIG. 12 of 3GPP TS 36.211 and shows the UL slot format for a generic frame structure.
As is described in Section 9.1 of 3GPP TR 25.814, the basic uplink transmission scheme is single-carrier transmission (SC-FDMA) with cyclic prefix to achieve uplink inter-user orthogonality and to enable efficient frequency-domain equalization at the receiver side. Frequency-domain generation of the signal, sometimes known as DFT-spread OFDM (DFT S-OFDM), is assumed.
FIG. 1B shows the generation of pilot samples. An extended or truncated Zadoff-Chu symbol sequence is applied to an IFFT block via a sub-carrier mapping block. The sub-carrier mapping block determines which part of the spectrum is used for transmission by inserting a suitable number of zeros at the upper and/or lower end. A CP is inserted into the output of the IFFT block.
In the PUCCH sub-frame structure for the UL control signaling, seven SC-FDMA symbols (also referred to herein as “LBs” for convenience) are currently defined per slot. A sub-frame consists of two slots. Part of the LBs are used for reference signals (pilot long blocks) for coherent demodulation. The remaining LBs are used for control and/or data transmission.
The current working assumption is that for the PUCCH the multiplexing within a PRB is performed using CDM and (localized) FDM is used for different resource blocks. In the PUCCH, the bandwidth of one control and pilot signal always corresponds to one PRB=12 SCs.
Two types of CDM are used both for data and pilot LBs. Multiplexing based on the usage of cyclic shifts provides nearly complete orthogonality between different cyclic shifts if the length of cyclic shift is larger than the delay spread of the radio channel. For example, with an assumption of a 5 microsecond delay spread in the radio channel, up to 12 orthogonal cyclic shifts within one LB can be achieved. Sequence sets for different cells are obtained by changing the sequence index.
Another type of CDM may be applied between LBs based on orthogonal covering sequences, e.g., Walsh or DFT spreading. This orthogonal covering may be used separately for those LBs corresponding to the RS and those LBs corresponding to the data signal. The CQI is typically transmitted without orthogonal covering.
Of particular interest to the exemplary embodiments of this invention is control channel signaling and, in particular, the use of the PUCCH.
As was noted, it has been determined in 3GPP that UEs having CQI transmission are code division multiplexed by means of different cyclic shifts of CAZAC sequences. In commonly owned and copending U.S. Provisional Patent Application No. 60/933,760, filed Jun. 8, 2007, by Kari Pajukoski, Esa Tiirola and Kari Hooli, entitled: Multi-code Precoding for CAZAC Sequence Modulation, Nokia Siemens Networks Oy Docket No.: 2007P02633, Harrington & Smith, PC Docket No. 863.0066.P1 (US), multi-code sequence modulation is provided to allow for larger CQI sizes, and a multi-code preceding for CAZAC sequence modulation is described.
One problem related to conventional CAZAC sequence modulation is the small spectrum efficiency per UE, due to the fact that only one modulated CAZAC sequence per UE can be transmitted during the long block. Correspondingly, the maximum symbol rate is limited to one symbol per block. Spectrum efficiency can be increased by transmitting multiple modulated CAZAC sequences simultaneously, however the use of this approach suffers from an increased PAR, which in turn results in either higher UE power consumption or decreased CQI coverage. The preceding method disclosed in U.S. Provisional Patent Application No. 60/933,760 significantly reduces PAR for multi-code sequence modulation. However, multi-code sequence modulation can still exhibit a larger PAR than single code sequence modulation.
3GPP has proposed the use of Zadoff-Chu sequences, as well as the extended and truncated modifications of Zadoff-Chu sequences, considered together with numerically searched CAZAC-like sequences. However, the multi-code sequence modulation has not been considered in the design of these sequences and one result of this is an increase in CM when multi-code sequence modulation is applied.
In 3GPP TSG RAN WG1 #49, Kobe, Japan, May 7-11, 2007, “Design of CAZAC Sequences for Small RB Allocations in E-UTRA UL”, Texas Instruments, R1-072206, a numerical search method for CAZAC-like sequences is presented. The method can be approximately summarized as follows:    1. A set of initial sequences are randomly selected with elements on the unit circle.    2. Sequences are iterated with two steps in a loop:            a. Sequences are forced to flat in frequency by dividing each sequence element with its amplitude; and        b. Sequences are forced to flat in time by dividing each sequence element with its amplitude.        
More specifically, R1-072206 describes a method for generating CAZAC sequences by computer search using random initialization. Because a random procedure is used to search these CAZAC sequences, they are referred to as Random-CAZAC. The procedure for generating the CAZAC sequence of length N is as follows:                (1) Let i=1, in the first step generate N QPSK random complex numbers:{tilde over (X)}if={{tilde over (x)}if(1), {tilde over (x)}if(2), . . . {tilde over (x)}if(n) . . . , {tilde over (x)}if(N)}; {tilde over (x)}if(n)ε{1+j, 1−j, −1+j, −1−j}.         (2) Next, define the sequence:        
            X      i      f        =                  {                                            x              1              f                        ⁡                          (              1              )                                ,                                    x              1              f                        ⁡                          (              2              )                                ,                      …            ⁢                                                  ⁢                                          x                1                f                            ⁡                              (                n                )                                      ⁢                                                  ⁢            …                    ⁢                                          ,                                    x              1              f                        ⁡                          (              N              )                                      }            =                        {                                                                                          x                    ~                                    i                  f                                ⁡                                  (                  1                  )                                                                                                                                        x                      ~                                        i                    f                                    ⁡                                      (                    1                    )                                                                                        ,                                                                                x                    ~                                    i                  f                                ⁡                                  (                  2                  )                                                                                                                                        x                      ~                                        i                    f                                    ⁡                                      (                    2                    )                                                                                        ,                          …              ⁢                                                          ⁢                                                                                          x                      ~                                        i                    f                                    ⁡                                      (                    n                    )                                                                                                                                                        x                        ~                                            i                      f                                        ⁡                                          (                      n                      )                                                                                                    ⁢              …                        ⁢                                                  ,                                                                                x                    ~                                    i                  f                                ⁡                                  (                  N                  )                                                                                                                                        x                      ~                                        i                    f                                    ⁡                                      (                    N                    )                                                                                                }                .              ⁢                        (3) Let sequence {tilde over (X)}it={{tilde over (x)}it(1), {tilde over (x)}it(2), . . . , {tilde over (x)}it(N)} be the IFFT of sequence {tilde over (X)}if, and define the sequence:        
      X    i    t    =            {                                    x            i            t                    ⁡                      (            1            )                          ,                              x            i            t                    ⁡                      (            2            )                          ,                  …          ⁢                                          ⁢                                    x              i              t                        ⁡                          (              n              )                                ⁢                                          ⁢          …                ⁢                                  ,                              x            i            t                    ⁡                      (            N            )                              }        =                  {                              (                                                                                x                    ~                                    i                  t                                ⁡                                  (                  1                  )                                                                                                                                        x                      ~                                        i                    t                                    ⁡                                      (                    1                    )                                                                                        )                    ,                      (                                                                                x                    ~                                    i                  t                                ⁡                                  (                  2                  )                                                                                                                                        x                      ~                                        i                    t                                    ⁡                                      (                    2                    )                                                                                        )                    ,                      …            ⁢                                                  ⁢                          (                                                                                          x                      ~                                        i                    t                                    ⁡                                      (                    n                    )                                                                                                                                                        x                        ~                                            i                      t                                        ⁡                                          (                      n                      )                                                                                                    )                        ⁢                                                  ⁢            …            ⁢                                                  ⁢                          (                                                                                          x                      ~                                        i                    t                                    ⁡                                      (                    N                    )                                                                                                                                                        x                        ~                                            i                      t                                        ⁡                                          (                      N                      )                                                                                                    )                                      }            .                      (4) Let the FFT of the sequence Xit be now denoted by {tilde over (X)}if; set i=i+1 and go back to step (2). Repeat the above steps (2), (3) and (4) for say M=1000 or more.        
For large number of iterations, it is said that it was found that the resulting sequence XMt is a CAZAC sequence. Further, several such CAZAC sequences can be generated by starting with a different random sequence in step (1) above.